A: Yes. The registration has to be signed on or before the date the petition is signed. And it has to be received by county elections officials on or before the date the petitions are turned in. Recall proponents said they will have voter registration forms with the petitions.

Q: Do I have to show ID to sign the petition?

A: No, but you will be required to print and sign your name, date the form and provide your address, which should match the address on your voter registration form.

Q: What if I sign more than one petition?

A: Only one of the signatures will count.

Q: What if I sign the petition and then change my mind?

A: You can withdraw your signature by filing a written request with the City Clerk before the petition is filed.

Q: Who will be collecting the signatures?

A: Initially, volunteers. More than 800 people have signed up. If necessary — and most political experts believe it will be — the campaign plans to use paid signature-gatherers, a common tactic in qualifying ballot measures. Gatherers typically are paid anywhere from 50 cents per signature to more than $6, depending on how hard it is to collect them and how late in the process they are needed.

Q: Where can I find petitions?

A: Sunday, kickoff events are planned at the Town and Country in Fashion Valley and a “Freedom from Filner” march at 2 p.m. at City Hall. Volunteers will also be in Balboa Park at the finish line of the America’s Finest City race.

Q: Where will petitions be located for the rest of the recall campaign?

A: “Wherever there are people,” according to campaign organizers: Chargers games, grocery stores, home-improvement centers, the usual petition places. They also hope to have people walking door-to-door in neighborhoods and are planning to put an interactive map on their website (recallbobfilner.com) where people can enter an address and find the location of the nearest signing spot. The website also has a way for people to receive petitions in the mail and send them back. To connect with people who live in San Diego but work in other cities, some signature gatherers will also be at gas stations or other businesses frequented by commuters.

Q: Will petitions be available online?

A: Organizers said they will make PDF versions of the petition available through their website. The PDF can be printed out and signed and then mailed back to the recall campaign.

Q: How many signatures are required?

A: They need 101,597 valid signatures. (That’s 15 percent of the city’s registered voters from the last election.) Organizers hope to collect 120,000 signatures to provide a cushion for the inevitable ones found invalid (people signing twice, people signing who aren’t eligible, people signing phony names).

Q: Is that a lot?

A: It is. According to Joshua Spivak, who writes The Recall Blog, only four recalls in the history of the U.S. that have needed that many signatures have made it to the ballot.

Q: How much time do they have to do it?

A: Thirty-nine days, another large hurdle. State law allows 160 days for recall petitions, but cities can adopt their own rules, and San Diego did, decades ago. When Poway voters recalled Councilwoman Betty Rexford three years ago, the signature-gatherers had 120 days.

Q: What happens when the petitions are turned in?

A: If there are not at least 101,597 signatures, the recall is dead. If that threshold is reached, the City Clerk has 30 days to validate the signatures. That is typically done through sampling, checking a certain number is see what percentage are valid.

Q: If the clerk’s review knocks the number of valid signatures below the necessary threshold, what happens?

A: Proponents will have another 30 days to collect more signatures. (They will also be allowed to collect signatures while the City Clerk is validating the initial batch of petitions.) If proponents are still short of the needed number then, the recall is over.

Q: If it qualifies for the ballot, when will the election be held?

A: Once the clerk certifies the petition and notifies the City Council, an election has to be scheduled for no less than 60 days and no more than 90 days later.

Q: What happens if the mayor resigns in between the time the petitions are certified and the election is held?

A: The recall election will be called off. A special election would then be held to replace him.

Q: Has San Diego ever had a recall election?

A: The only one since the City Charter was adopted in 1931 was in 1991, when about 71 percent of the voters in Councilwoman Linda Bernhardt’s district backed her recall.

Q: What does recent history say will happen if the recall qualifies for the ballot?

A: Every election is different. Last year, nationwide, there were 168 recall elections. Of those, 108, or about 65 percent, succeeded.

Q: If Mayor Filner is recalled, what happens?

A: Candidates hoping to replace him will be on the same ballot as the recall. The one who gets the most votes, even if it’s not a majority, will succeed Filner and serve out the rest of his term.

Q: Can Filner run?

A: No. If he is recalled, he would have to wait at least a year to run again for mayor.

Q: What kind of legal challenges are possible?

A: City law allows only those who vote for the recall to then vote for a replacement. A similar provision was ruled unconstitutional during the Gov. Gray Davis recall in 2003. The City Council is expected to consider a revision soon. There are other technical provisions of the law that some legal experts believe are subject to interpretation, which opens the door for litigation. Spivak, the recall blogger, calls San Diego’s recall law a “disaster” and said it ranks “among the worst recall laws in the country, if not the globe.”